The present invention relates to an electromagnet and as well to an actuating mechanism using thereof for a switching device, and in particular to an electromagnet for restraining demagnetization of a permanent magnet, and as well to a reliable operating mechanism using thereof for a switching device.
Related Art
As to the actuating mechanism for a switching device, there have been provided an electric power driven spring actuating mechanism, and a hydraulic or pneumatic actuating mechanism. These mechanism have a large number of components so as to have a link mechanism which is complicated, resulting in a relatively high manufacturing cost. An operating mechanism using an electromagnet is used as one of measures for simplifying the link mechanism. For example, JP-A-5-234475 discloses a vacuum contactor in which an electromagnet is used for turn-on operation so that a closing spring which has been stored with energy is released simultaneously with the turn-on operation in order to open contacts. Further, in an actuating mechanism disclosed in JP-A-10-249092, a plunger is provided extending through two turn-on and -off coils so that both turn-on and turn-off are carried by electromagnet. Further, JP-A-2000-249092 discloses an actuating mechanism which maintains a turn-on condition with the use of an attraction force of a permanent magnet, and turn-off operation is carried out with the use of springs for driving movable members, which are provided respectively, by reversely energizing a coil with coil current. In this case, it is advantageous since only a single coil is required for both turn-on and turn-off.
However, the conventional electromagnet incorporating a permanent magnet has raised following disadvantages: a permanent magnet may be a rare-earth samarium cobalt group magnet, a neodymium group magnet, an alnico group magnet, a ferrite group magnet or the like. If the neodymium group magnet which has a high residual magnetic flux density and which has a relatively low cost is used, an electromagnet can be small-sized and manufactured at a relatively low cost. However, the neodymium group magnet has a high magnetic coercive force, that is, 1,000 KA/m so as to require a magnetized electric field which is higher than 2,000 KA/m (corresponding to a magnetic flux density of 2.5 T). Accordingly, it is unpractical to magnetize a permanent magnet with a coil of an incorporated electromagnet, and accordingly, a magnet has to be incorporated after being magnetized.
In the case of application of an electromagnet for a actuating mechanism for a switching device, reliable operation for a long term greater than 20 years and by a huge number of operating times are required. Accordingly, factors which cause demagnetization of a permanent magnet should be eliminated as possible as it can. An electromagnet incorporating a permanent magnet as disclosed in the JP-A-2000-249092, a backing magnetic field is applied to the permanent magnet, direct thereto so as to carry out cut-off operation. The repetition of application of reverse energy to the permanent magnet causes a risk of demagnetization of the permanent magnet or lowering of the use life thereof.
Further, if a permanent magnet is present on a magnetic path, a magnetic resistance as viewed from a coil becomes higher. Since the permeability of a permanent magnet is substantially equal to that of the air, a gap which is equal to a sum of a stroke length and the thickness of the permanent magnet is present at the time of a start of operation, and accordingly, a greater ampere turn is required.
Further, metrication errors caused during manufacture are inevitable for the thickness of the permanent magnet and the core, and the gap between the permanent magnet and the movable core which is opposed to the former and which can extend and retract, at an end of the stroke of the latter varies. Further, this gap causes the turn-on characteristic, the cut-off characteristic and the turn-on condition holding force (attraction force) to vary. However, should the allowable range for metrication errors, that is, the tolerance be strictly managed, the manufacture of an inexpensive electromagnet could be hardly be produced.
The present invention is devised in order to solve the above-mentioned problems, and an object of the present invention is to provide an electromagnet having a long use life and a high degree of efficiency, in which no backing magnetic field is applied to a permanent magnet, and further, no permanent magnet is present in a magnetic path which is created by a coil current, and as well to provided an actuating mechanism for a switching device, using the electromagnet.
Another object of the present invention is to provide an electromagnet in which the gap between the permanent magnet and the movable core which is opposed to the former and which can extend and retract can be simply adjusted.
According to the present invention, there is provided an electromagnet comprising a coil, a movable iron core which is moved on the center axis of the coil, a stationary iron core which is provided so as to cover upper, lower and outer peripheral surfaces of the coil, and a permanent magnet located in a gap defined by the movable iron core and the stationary iron core, wherein the movable core is attracted to the stationary core by a magnetic field produced by the permanent magnet.
Further, according to the present invention, there is provided an electromagnet comprising a coil, a movable iron core which is moved on the center axis of the coil, a stationary iron core which is provided so as to cover upper, lower and outer peripheral surfaces of the coil, the stationary core is provided, on such a side that the movable iron core is inserted, with a magnetic protrusion, and the movable iron core being composed of a plunger and a steel plate secured to one end part of the plunger so that an end face of the plunger and the stationary iron core, and the steel plate and the protrusion are opposed to each other in the same directions, respectively, and a permanent magnet provided in a zone which is defined by the plunger, the protrusion, the steel plate and the stationary iron core.
Further, according to the present invention, there is provided an electromagnet comprising a coil, a movable iron core which is moved on the center axis of the coil, a stationary iron core which is provided so as to cover upper, lower and outer peripheral surfaces of the coil, the stationary core is provided, on such a side that the movable iron core is inserted, with a magnetic protrusion, the movable iron core being composed of a plunger and a steel plate secured to one end part of the plunger, and a permanent magnet provided in a gap defined by the plunger, the protrusion, the steel plate and the stationary iron core, a side surface of the steel plate and the protrusion being opposed to each other, and an end face of the plunger and the stationary iron core, and the steel plate and the permanent magnet being opposed to in the same direction, respectively.
Further, according to the present invention, there is provided the electromagnet as mentioned above, which incorporates a power source circuit for selectively applying a forward or reverse current to the coil, and accordingly, when the forward current is applied, a magnetic field is produced in a direction the same as a direction of a magnetic field produced by the permanent magnet so as to effect attraction, and when the reverse current is applied, the magnetic field produced by the permanent magnet is cancelled so as to effect release action.
Further, according to the present invention, there is provided an electromagnet including a coil, a movable iron core which is moved on the center axis of the coil, a stationary core configured to cover both axially end surfaces and the outer peripheral surface of the coil, and a power source for applying a forward current and a reverse current to the coil, wherein the movable iron core is moved toward the stationary core when the forward current is applied to the coil, characterized in that the stationary iron core includes an iron core upper member configured to cover one of the axial end surfaces of the coil, a permanent magnet is located on the upper surface of the stationary iron core upper member while the movable iron core includes a planer plate member having a surface opposed to the upper surface of the stationary iron core with the permanent magnet intervening therebetween, and a plunger member having a cylindrical surface opposed to the inner peripheral surface of the coil, the inner peripheral surface of the stationary iron core upper member and the cylindrical surface of the plunger member defines therebetween a gap g1 which is smaller than the axial thickness t of the stationary core of the permanent magnet.
A magentic member may be interposed between the end surface of the plunger member on the planer plate side, and the planar plate member.
The permanent magnet may be the one selected from a group consisting of a rare earth samarium-cobalt group magnet, an alnico group magnet a ferrite group magnet.
Further, according to the present invention, there is provided an actuating mechanism for a switching device, incorporating the above-mentioned electromagnet, separatable contacts, a cut-off spring for opening the contacts, a power source circuit for selectively applying forward and reverse current to the coil wherein when the forward current is applied, the cut-off spring is urged while the contacts are turned on so as to hold the turn-on condition by attraction force of the permanent magnet, and when the reverse current is applied to the coil, a magnetic field produced by the permanent magnet is cancelled out so that the opening and closing device is cut off by a force of the cut-of spring.
That is, with the electromagnet, constituted as mentioned above, in which a magnet field causing a reverse current to run through the coil does never extend through the permanent magnet upon cut-off, the permanent magnet can be prevented from being reversely excited and further, no permanent magnet is present in a magnetic path created by coil current so that no factor of demagnetizing the permanent magnet is present, resulting in the possible use of a neodymium group magnet, thereby it is possible to provide an electromagnet having a long use life and a high degree of efficiency.
Further, by changing the thickness of a magnetic member interposed between the end surface of the plunger member on the planer plate member side, and the planer plate or changing the number of thin planar plate members which constitute the magnetic member, the gap between the permanent magnet and the movable iron core which is opposed to the former and which can extend and retract, at a stroke end, can be adjusted. That is, the characteristics thereof can be stabilized without causing the tolerance of components of the permanent magnet to be strict, thereby it is possible to provide an inexpensive electromagnet with a high degree of accuracy.
Further, with the application of the electromagnet in the actuating mechanism for a switching device, the switching device can be small-sized and inexpensive and can offer a high degree of reliability.
The present invention will be detailed in the form of preferred embodiments with reference to the accompanying drawings.